A study in the journal Language finds that even though different languages sound like they run at different speeds, the average information conveyed by each over a constant period of time is more or less equivalent.

I wonder if this is constant is a result of the transmission limits of the speaker or of the processing capabilities of the listener? Or both?

This finding reminded me of the odd fact that the average lifespan of amphibians, birds, fish, mammals, reptiles, and humans all cluster around one constant: the total number of heartbeats. That is, while all those animals live different life spans in terms of years, all average about 1 billion heartbeats. Animals that live for fewer years, on average, tend to have really high average heart rates, while animals that tend to outlive humans have slower heart rates. The mass of the animal seems to play a role. In the animal kingdom, larger species tend to have slower pulse rates and longer life spans.

While there isn't complete consensus around why this is, one oft-cited explanation is Kleiber's law. The theory is that the internal networks needed to distribute nutrients across an animal's structure achieve certain economies of scale. Mathematical models have found the same scaling efficiency as has been measured in the animal kingdom.